Rotational rate or yaw sensors are typically used in order to determine an angular velocity or rotational rate of an object about an axis. If the rotational rate sensor is produced micromechanically on the basis of a silicon substrate, it offers the advantage, for example relative to a gyroscope manufactured by precision engineering, that it can be produced with very small dimensions at relatively low costs. A relatively small measuring uncertainty and a small energy consumption during the operation are further advantages. An important area of application of rotational rate sensors is in the field of automobile technology, for example in connection with driving dynamics regulation systems such as the electronic stability program (ESP). In that regard, an anti-lock system, an automatic braking force distribution, a drive or traction slip regulation, and a yaw moment regulation operate cooperatively so that a transverse and lengthwise stabilization of the motor vehicle is achieved by the targeted braking of individual wheels. Thereby it is possible to prevent a rotation of the motor vehicle about its vertical axis. A further application for rotational rate sensors is in the so called rollover detection of a motor vehicle in connection with airbag control units and restraint systems for vehicle passengers. Furthermore, rotational rate sensors are used for navigation purposes as well as for the determination of the position or orientation and the state of motion of motor vehicles of all types. Other fields of use are, for example, image stabilization devices for video cameras, dynamic regulation of satellites during deployment or insertion into the earth orbit path, or in civil air traffic in backup position regulation systems.
Micromechanically produced rotational rate sensors generally comprise a seismic or inertial mass, which is set into an oscillation or vibration by an excitation means. If the seismic mass in a rotating system moves radially inwardly or outwardly, then its path or trajectory velocity changes. It thus experiences a tangential acceleration, which is caused by the Coriolis force. The reaction of the seismic mass to the rotation can be detected, for example, by means of a read-out arrangement.
The international publication WO 03/104823 A1 discloses a multi-axis monolithic acceleration sensor with up to four seismic masses, that are embodied in the form of paddles and are suspended via torsion springs on a frame. With this sensor, accelerations in the direction of the respective main sensitivity axes, but no rotational rates or speeds, can be measured.
From the German patent DE 196 41 284 C1, a micromechanical rotational rate sensor is known, with a substrate, a base element suspended by several spring elements on the substrate, an excitation means and a read-out arrangement, wherein the base element comprises a seismic mass and the spring element is embodied as a linear spring. Such micromechanically produced rotational rate sensors are preferably etched out of a silicon block. Thereby, even very small deviations in the manufacturing accuracy lead to flank angles of the respective structures. During a deflection of the spring elements, the flank angles cause a motion of the base element perpendicular to its excitation, thus namely in the measuring direction of the rotational rate sensor. This leads to very high demands or requirements on the manufacturing accuracy, or to a very high reject rate of the structures that are, for example, etched out of a silicon wafer. Moreover, complex or costly electronic evaluating circuits are required in order to compensate the measuring inaccuracies caused by the flank angles.